This research study encompasses a range of phenotypes that include Pallister-Hall syndrome, the allelic disorder Greig cephalopolysyndactyly syndrome (GCPS), McKusick-Kaufman syndrome (MKS), and Bardet-Biedl syndrome (BBS). The clinical manifestations of these disorders include polydactyly, central nervous system malformations (with or without mental retardation and seizures), craniofacial malformations, and visceral malformations such as renal malformations or congenital heart defects. We study these disorders by a translational approach that begins in the clinic with careful clinical evaluation of the phenotypes by physical examination, imaging studies that include radiographs, ultrasound, MRI and CT scanning. We have recently determined that BBS and MKS can both be caused by mutations in the same gene. In addition, we have shown that in GCPS, patients with large deletions are more likely to have developmental delay or delayed speech. These data will be used to develop additional hypotheses that can be investigated at the clinical or molecular level.